1. Field of the Invention
The present invention relates generally to optically recordable carriers and, more particularly, is directed to an optically recordable carrier having an optical record layer covered with a protective film.
2. Description of the Prior Art
An optically recordable medium particularly suited for use in a magneto-optical recording system is known in which a thin film of an alloy of rare earth metal and transition metal or the like is provided on a substrate. For example, amorphous films, such as, GdCo. GdFe, TbFe, DyFe, GdTbFe, TbDyFe and so on, have been proposed for use as optical record layers. In general, these known optically recordable media have poor corrosion resistance so that they are easily corroded in a humid atmosphere, and their characteristics as a record medium are deteriorated.
In order to prevent a metal layer on an optical disc from being corroded, it has been proposed by a person owing a duty to assign to the assignee of the present application, for example, as disclosed in U.S. patent application Ser. No. 06/693,303, filed Jan. 23, 1985, and which is a continuation application of Ser. No. 06/363,532, filed on Mar. 30, 1982, now abandoned, to omit the metal optical record layer from an outer edge portion and/or an inner edge portion of a substrate and to provide a protective film of organic material which extends over the metal optical record layer to the outer edge portion and/or the inner edge portion of the substrate. It is intended that the foregoing protective film of organic material will prevent the metal optical record layer from being exposed to the atmosphere and thus will prevent corrosion of the optical record layer.
However, even when the metal optical record layer is excluded from the outer edge portion and/or inner edge portion of the substrate and the metal optical record layer is covered with a protective film of organic material, such protective film of organic material cannot completely seal out water vapor and oxygen. There is still the risk that water vapor and oxygen in the atmosphere will be diffused through the protective film of organic material and reach the metal optical record layer. Thus, complete protection of the optical record layer from corrosion cannot be attained. Corrosion of the optical record layer is, of course, a particularly serious problem in the case of optically recordable carriers which are employed in magneto-optical recording and reproducing systems of the type in which recording, reproduction and erasure are carried out repeatedly.